60. Solving a chemistry problem

13. A portion of the sulfamide preparation was dissolved in 10 ml of dilute hydrochloric acid and the analyzed solution was obtained, which was diluted with distilled water to 100 ml and the test solution was obtained. Potentiometric titration of the test solution with a standard 0.05 mol/l sodium nitrite solution was carried out and the following results were obtained (V is the volume of the added titrant, E is the EMF of the circuit):
V, ml 15 15.05 15.10 15.15 15.20 15.25
E, mV 320 340 450 568 610 615
Determine the molar concentration of the sulfa drug in the analyzed solution.
Answer: 7.575*10-2 mol/l